Turbomachine and impeller

ABSTRACT

Turbomachine for increasing the pressure of a fluid or mixture of fluids, comprising an inlet and an outlet, a casing, a rotatable shaft arranged in the casing, diffusers or similar operatively arranged in the turbomachine, and a means for rotation operatively connected to the shaft. The turbomachine is distinguished in that it comprises: at least one impeller of a mixed flow type arranged on the shaft, the impeller having an inlet and an outlet, the inlet is closer to an axis of rotation than the outlet; and at least one further impeller arranged on a common or operatively connected shaft, chosen from the group consisting of axial impellers arranged upstream of the mixed flow type impeller and radial impellers arranged downstream of the mixed flow type impeller. Impeller for use in a turbomachine for increasing the pressure of a fluid or mixture of fluids, the impeller comprising at least one blade, distinguished in that it comprises at least one fluid passageway fluidly connecting the pressure side of the blade with the leeward side of the blade.

FIELD OF THE INVENTION

The present invention relates to equipment for increasing the pressureof a fluid or a mixture of fluids, such as a mixture of oil, water andgas. More specifically, the invention relates to a turbomachine forincreasing the pressure of a fluid or mixture of fluids and an impellerfor use in a turbomachine.

BACKGROUND OF THE INVENTION AND PRIOR ART

A turbomachine is a machine that transfers energy between a rotor and afluid, the energy is added as kinetic energy to the fluid or retrievedas kinetic energy from the fluid. Turbomachinery is a large group ofmachinery of which flow-machines is one type. For flowmachines havingrotors, such as centrifugal pumps and compressors, the added kineticenergy is associated with an increased static pressure as the kineticenergy of the fluid is converted in means used for such purpose, such asa diffuser, a volute section or similar means. The rotors offlowmachines are usually the blades of one or more impellers. Theimpellers are usually arranged in series on a shaft, the number ofimpellers in series is determined by the required delivery pressure.

When oil, gas, condensate and inevitably also often water and possiblysand is produced from a hydrocarbon reservoir below a seabed, aturbomachine able to increase the pressure of such complex and usuallyvariable mixture is very useful. Such turbomachines can be located on aseabed at a wellhead and even downhole in a production well. Apart fromsevere problems caused by possible contents of sand in the mixture, thegas contents impose problems for the turbomachine, as the efficiencytends to be severely reduced with increased gas volume fraction (GVF) inthe mixture. Some such turbomachines exist and they are usually calledmultiphase pumps. Such multiphase pumps consist of axial flow typeimpellers or axial flow type impellers combined with radial flow typeimpellers, as described in U.S. Pat. Nos. 4,365,932, 5,375,976,5,885,058, 5,961,282, 6,474,939, 5,562,405, 5,253,977 and 6,547,514, andin the patent publication JP 10288199. In U.S. Pat. No. 6,547,514 thefirst pump stage is called a helicoaxial pump, but said pump consists ofhelical impellers (paragraph 0021 and claim 10) for which most of theflow particles follow an axial path, for which reason the impellers orpump stage is of axial flow type but having a slightly tapered hub,which is known also for other axial impellers or pumps. From U.S. Pat.No. 5,885,058 teaching is provided (FIGS. 3, 4 and 6, col. 10 lines4-13, col. 11 lines 14-24) in order to have a remixing action for gashaving tendency to accumulate at certain places of the impeller, butonly as a specific twin blade construction and a specific twin bladeconstruction with perforations coaxial to a circle of rotation.

For further information about the turbomachines suitable for operationwith multiphase fluid, reference is made to the patent publicationsmentioned above.

In spite of the available technology as mentioned above, there is ademand for alternative turbomachines and impellers, particularlyturbomachines and impellers that can tolerate more variations withrespect to the composition of fluid mixtures, particularly the contentsof gas, while still reliably delivering high pressure and highthroughput. The objective of the present invention is to meet saiddemand.

SUMMARY OF THE INVENTION

The objective is met by providing a turbomachine for increasing thepressure of a fluid or mixture of fluids, comprising an inlet and anoutlet, a casing, a rotatable shaft arranged in the casing, diffusers orsimilar operatively arranged in the turbomachine, and a means forrotation operatively connected to the shaft. The turbomachine isdistinguished in that it comprises

-   -   at least one impeller of a mixed flow type arranged on the        shaft, the impeller having an inlet and an outlet, the inlet is        closer to an axis of rotation than the outlet, and    -   at least one further impeller arranged on a common or        operatively connected shaft, chosen from the group consisting of        axial impellers arranged upstream of the mixed flow type        impeller and radial impellers arranged downstream of the mixed        flow type impeller.

The simplest version of the turbomachine of the invention comprises oneimpeller of a true mixed flow type on a rotatable shaft in a casing orhousing, and one of the further impellers. The impeller is a true mixedflow type impeller if all flow particles or all of the fluid follow apath having both an axial and a radial component, from the inlet to theoutlet, which in this context is defined by having the inlet closer toan axis of rotation than the outlet, preferably all of the inlet closerto an axis of rotation than the outlet. Accordingly, the inner part ofthe outlet is preferably outside the outer part of the inlet, measuredfrom the axis of rotation. Also, the outlet is further down the axis ofrotation than the inlet for a mixed flow type impeller. For axialimpellers, the flow particles have only an axial component of the pathof flow for at least a part of the flow or path of flow, whilst forradial impellers the flow particles have only a radial component for atleast a part of the flow or path of flow.

The turbomachines or multifluid pumps of the invention comprises animpeller of true mixed flow type, in combinations not previously knownwith one or more of the further impellers. More specifically, in theturbomachine, following the path of fluid flow from the inlet to theoutlet: one or more axial impellers are arranged, followed by one ormore mixed flow type impellers, followed by one or more radialimpellers, which embodiment is preferable for high to moderate gasvolume fractions (GVF) and high pressure requirement. Alternatively,following the path of fluid flow from the inlet to the outlet: one ormore axial impellers are arranged, followed by one or more mixed flowtype impellers, which embodiment is most preferable for very high gasvolume fractions. Alternatively, following the path of fluid flow fromthe inlet to the outlet: one or more mixed flow type impellers arearranged followed by one or more radial impellers, which embodiment ispreferable for moderate gas volume fractions and high pressurerequirement. The term one or more covers any integer from one to as manyas required to deliver the required pressure or gas compression, such as1 to 5, 10 or 15. Accordingly, the turbomachines of the invention arecapable of subsea and/or downhole pumping and compressing a liquid/gasfluid mixture of very high GVF to very high pressure.

The turbomachine preferably includes several impellers, preferably alsoof the further or different types and with appropriate diffusers orsimilar arranged between stages or impellers in order to convert thekinetic energy into pressure. The diffusers or similar means can be apart of the casing or housing or be arranged on the shaft between stagesor impellers, in the form of diffusers, stators, rectifiers, adjustersor volute chambers or other means known per se. The shaft can be dividedinto several releasable and thereby replaceable sections preferablycoaxially connected. The casing can be divided into several parts, alsoinner and outer parts. The means for rotation is for example a motor ofany appropriate type. The concept of having axial impellers arrangedupstream of the mixed flow impeller and radial impellers arrangeddownstream of the mixed flow impeller has to do with the tolerance forhandling gas and the capability to deliver high pressures and highthroughput reliably. More specifically, the axial impellers can toleratemore gas, but deliver less pressure while the radial impellers cantolerate less gas but deliver higher pressure, relative to the mixedflow type impeller. Accordingly, high tolerance for gas can be achievedand high pressure can be achieved, since the gas can be successivelycompressed and the gas volume fraction can be successively reduced to alevel that can be handled effectively by the next stage or impeller.

Preferably, the mixed flow type impeller is of a particular constructionfavorable with respect to tolerate gas, and preferably one or severalfeatures improving the tolerance for gas is included in some or all ofthe impellers, particularly the leading or upstream impellers operatingat the highest gas volume fractions.

Accordingly, the turbomachine, comprising impellers with impellerblades, preferably comprises fluid passageways arranged so as to fluidlyconnect the pressure side of a blade with the leeward side of the blade,in order to have remixing of gas and liquid, said fluid passageways arepreferably chosen amongst perforations arranged close to or at the inneredge of the blades, gaps between the blade or shroud and a hub or shaft,and fluid passageways arranged in the hub or shaft. Preferably one ormore of the impellers, particularly the impellers of mixed flow type,comprises a hub arranged on or integral with the shaft and a shroud withblades arranged outside the hub around the periphery on and toward theinlet side of the hub and impeller, a gap is provided between the huband the shroud, the gap is formed between the inner surface of theshroud and the outer surface of the hub, from the inlet side of theimpeller, the gap preferably has the shape of a cylindrical or conicalshell or helix-shaped band.

Preferably at least some impeller blades are perforated, and forimpellers having several blades or pressurized volumes between blades,the perforations are not coaxial as seen parallel to the shaft.Preferably impeller blades are perforated for a number of blades, saidperforations are not coaxial as seen along a circle crossing the blades,said circle being coaxial and perpendicular to the axis of rotation.Said non-coaxial arrangements will improve the remixing of gas withliquid since successive pockets of gas between blades can be avoided byarranging perforations in order to eliminate “neighbour” gas pockets.Further, at least some impellers have blades preferably having aclearance in between the blades at the portion close to the shaft, asseen parallel to the shaft, preferably said clearance, as seen along aline parallel to the shaft, in substance has the shape of a trianglehaving a small apex angle, and it represents a leakage passageway forfluid to remix gas and liquid.

The invention also provides an impeller for use in a turbomachine forincreasing the pressure of a fluid or mixture of fluids, particularlyfeasible for use in a turbomachine according to the present invention.The impeller comprises at least one blade and is distinguished in thatit comprises at least one fluid passageway fluidly connecting thepressure side of the blade with the leeward side of the blade,preferably across the blade or around the inner edge of the blade.Preferably the fluid passageway is chosen amongst perforations arrangedclose to or at the inner edge of the blade, such as within one bladewidth from the inner edge of the blade, gaps between the blade or shroudand a hub or shaft, and fluid passageways arranged in the hub or shaft.Preferably the impeller blades are perforated for at least a number ofblades, preferably said perforations are not coaxial neither as seenalong a circle crossing the blades, said circle being coaxial andperpendicular to the axis of rotation, nor as seen along an axisparallel to the shaft.

In a preferable embodiment of the invention the impeller is of a mixedflow type, distinguished in that it comprises: an inlet and an outlet,the inlet is closer to an axis of rotation than the outlet; a hubarranged on or integral with a shaft, and a shroud with blades arrangedoutside the hub around the periphery thereof; and a gap is providedbetween the hub and the shroud. Preferably the gap is formed between theinner surface of the shroud and the outer surface of the hub, from theinlet side of the impeller, the gap preferably has the shape of acylindrical or conical shell or helix-shaped band. Said gap represents aleakage passageway for fluid to remix gas and liquid. Preferably thewhole inlet is closer to an axis of rotation than the outlet.Accordingly, all flow particles or all of the flowing fluid preferablyflow out from the outlet further away from an axis of rotation than theinlet. The angle of flow is preferably axial (i.e. parallel to theshaft) for the inlet and about 10° to 70° from axial for the outlet. Theflow particles can be seen as a fluid molecule or particle defining atrajectory of flow as it flows through the impeller in operation. Thehub is preferably conical and widest at the downstream or trailing side,allowing the shroud to be fastened easily at the downstream or trailingside of the hub by threads or by other convenient means, whilst the gapis formed between the interfaces upstream, which design is preferablealso for the further impellers.

Preferably the impeller blades are having a clearance in between them atthe portion close to the shaft, for a number of impellers, as seenparallel to the shaft, said clearance, as seen along a line parallel tothe shaft, in substance preferably has the shape of a triangle having asmall apex angle.

Any operative combination of the turbomachine of the present invention,as defined in a respective independent claim, with features mentioned orillustrated in this document, is a part of the invention. Any operativecombination of the impeller of the present invention, as defined in arespective independent claim, with features mentioned or illustrated inthis document, is a part of the invention.

FIGURES

The present invention is illustrated with seven figures, of which

FIG. 1 illustrates a turbomachine of the present invention,

FIG. 2 illustrates a further turbomachine of the present invention,

FIG. 3 illustrates an impeller of the present invention,

FIG. 4 illustrates comparative flow data through impellers of and not ofthe present invention,

FIG. 5 illustrates comparative flow data through impellers of and not ofthe present invention,

FIG. 6 illustrates flow through an impeller not of the presentinvention, and

FIG. 7 illustrates flow through an impeller of the present invention.

DETAILED DESCRIPTION

Reference is made to FIG. 1 illustrating an embodiment of a turbomachine1 according to the present invention. More specifically the turbomachine1 comprises an inlet 2 and an outlet 3, a casing 4 and a rotatable shaft5 arranged in the casing, diffusers 6 or similar operatively arranged inthe turbomachine, and a means 7 for rotation operatively connected tothe shaft. The illustrated turbomachine comprises three impellers 8 of amixed flow type arranged on the shaft, the impeller having an inlet andan outlet, the inlet is closer to an axis of rotation than the outlet;three axial impellers 9 arranged upstream of the mixed flow typeimpeller and three radial impellers 10 arranged downstream of the mixedflow type impeller.

Reference is made to FIG. 2 illustrating a further turbomachine 1 of thepresent invention, more specifically a longitudinal section thereof. Thesame reference numericals as used in FIG. 1 are used for identical orsimilar features also in FIG. 2. The turbomachine of FIG. 2 comprisestwo impellers 8 of mixed flow type, arranged on the shaft toward theinlet 2, and seven radial impellers 10. The radial impellers 10 are fromleft to right three impellers, then the flow is directed to the radialimpeller at the very end of the shaft, from where the flow successivelyis directed through the remaining radial impellers back along the shaft,to the very last impeller below the outlet 3. This arrangement improvesthe stability of the turbomachine by balancing out axial forces. Forclarity, only some of the diffusers are referenced numerically. The flowbores are not possible to follow all the way on a 2D section, however a3D animation or a large number of successive sections would allow theflow bores to be followed through the machine. The means for rotation isnot particularly relevant in this context and is known per se, and isnot illustrated. The diffusers, bearings, shaft seals and other featuresare not particularly relevant in this context either, and are also knownper se, and are therefore not discussed in further detail.

Reference is made to FIG. 3 illustrating an impeller of the presentinvention, more specifically a longitudinal section of a mixed flow typeimpeller 8. The impeller comprises an inlet 11 and an outlet 12, theinlet is closer to an axis of rotation, indicated by a dotted line, thanthe outlet. A hub 13 is arranged on or integral with a shaft, and ashroud 14 with blades is arranged outside the hub around the peripheryand facing the inlet side of the impeller. A gap 15 or slit is providedbetween the hub and the shroud.

Further reference is made to FIGS. 4 and 5, illustrating head andefficiency at 100% and 120% of BEP (Best Efficiency Point),respectively, with and without a fluid passageway in the form of a gap(hub blade clearing), as a function of GVF (Gas Volume Fraction) at thepump inlet. The lines marked with “diamond” symbols represent head H andthe lines marked with triangles represent efficiency Eta. The dottedlines represent data for an impeller according to the invention, with ahub gap. The solid lines are for an identical impeller outside theinvention, without a hub gap. An increase in head is generated for GVFbetween 5 and 40% at 100% of BEP. A very significant increase in head isgenerated for GVF above about 5% at 120% of BEP. This illustrates a partof the technical effect of the invention.

Further reference is made to FIGS. 6 and 7, illustrating accumulated gasvolume fraction in a cross section in the middle of the flow channel,with and without a gap, respectively. The gas volume fraction isillustrated by a grey scale, the darker the tone the higher GVF. In FIG.6, without a gap and not according to the present invention, the highestGVF is in the corner between the hub and the blade. In FIG. 7, with agap and according to the invention, it is clearly illustrated how, dueto the gap, gas is redistributed or remixed, and the pressure side ofthe blade is practically free of accumulated gas or air, which isassumed to be crucial for good efficiency. In the figures, the blade isslightly inclined from the horizontal and almost parallel to the Y-axis,whilst the hub is on the left side at about 45° inclination from theblade.

Several other results exist able to demonstrate the technical effect ofthe invention, from simulations, calculations and tests, for both theturbomachine and the impeller.

For both the turbomachine and the impeller of the invention, preferablygaps are provided, and perforations and clearances, which featuresprovide remixing of gas and liquid, thereby avoiding gas pocketsblocking or disturbing the flow, the beneficial effect of remixingexceeding any reduction in pumping or compression effect due the“leakage” flow over said gaps, perforations and clearances. By followingthe teaching of the current document, and good engineering practice,said preferable embodiments are achievable based on calculations,modelling and testing for specific applications in order to find thecorrect places and sizes for gaps, perforations and clearances.

For a turbomachine of the invention, for almost any specific embodimentand application, the length of the shaft can be reduced compared toprior art equipment, which results in improved reliability, reduced sizeand weight and reduced power consumption, in addition to greatertolerance as to gas volume fraction or variation. Dependent on thespecific embodiment, the turbomachine can operate efficiently at above80% GVF input and deliver fluid at pressures over 200 bar. The mixedflow stage or impeller is capable of handling GVF of 50% or even higher,and is favourable for a GVF range of about 50-20%. Each impellerincreases the pressure with about 20 bar, decreasing with increasingGVF. For a turbomachine required to handle higher GVF than about 50%, apre-stage of axial impellers are preferably included. For high pressuredelivery, radial impellers are preferably used downstream of the mixedflow type impellers after the GVF has been compressed to about 15% orlower.

1. A turbomachine for increasing the pressure of a fluid or mixture offluids, comprising: an inlet and an outlet; a casing; a rotatable shaftarranged in the casing; diffusers or similar operatively arranged in theturbomachine; a means for rotation operatively connected to the shaft;and at least one impeller with at least one blade, wherein theturbomachine comprises: at least one fluid passageway connecting apressure side of an impeller blade with a leeward side of the impellerblade, the at least one fluid passageway is arranged so as to haveremixing of gas and liquid by having in substance gas flowing throughthe at least one fluid passageway.
 2. The turbomachine according toclaim 1, wherein the at least one fluid passageway is chosen amongstperforations arranged close to or at the inner edge or end of theblades, within one blade width from the inner edge or end of the blade,gaps between the blade or shroud and a hub or shaft, and fluidpassageways arranged in the hub or shaft.
 3. The turbomachine accordingto claim 1, wherein one or more of the impellers comprises a hubarranged on or integral with the shaft and a shroud with blades arrangedoutside and around the periphery of the hub, and a gap is providedbetween the hub and the blades of the shroud.
 4. The turbomachineaccording to claim 1, wherein following the path of fluid flow from theinlet to the outlet: one or more axial impellers are arranged, followedby one or more mixed flow type impellers, followed by one or more radialimpellers.
 5. The turbomachine according to claim 1, wherein followingthe path of fluid flow from the inlet to the outlet: one or more axialimpellers are arranged, followed by one or more mixed flow typeimpellers.
 6. The turbomachine according to claim 1, wherein followingthe path of fluid flow from the inlet to the outlet: one or more mixedflow type impellers are arranged, followed by one or more radialimpellers.
 7. The turbomachine according to claim 1, wherein at leastsome impeller blades are perforated, and for impellers having severalblades the perforations for neighbor blades are not coaxial as seenparallel to the shaft.
 8. The turbomachine according to claim 1, whereinimpeller blades are perforated for a number of blades, and for impellershaving several blades the perforations of neighbour blades are not onthe same circle of rotation around the shaft.
 9. The turbomachineaccording to claim 1, wherein at least some impellers have blades havinga clearance in between the blades at the portion close to the shaft,preferably said clearance for neighbor blades as seen along a lineparallel to the shaft, in substance has shape of a triangle having asmall apex angle.
 10. An impeller for use in a turbomachine forincreasing the pressure of a fluid or mixture of fluids, the impellercomprising: at least one blade; and wherein the turbomachine comprisesat least one fluid passageway connecting the pressure side of a bladewith the leeward side of the blade, the at least one fluid passageway isarranged so as to have remixing of gas and liquid by having in substancegas flowing through the fluid passageway.
 11. The impeller according toclaim 10, wherein the at least one fluid passageway is chosen amongstperforations arranged close to or at the inner edge or end of theblades, within one blade width from the inner edge or end of the blade,gaps between the blade or shroud and a hub or shaft, and fluidpassageways arranged in the hub or shaft.
 12. The impeller according toclaim 10, wherein the impeller comprises: an inlet and an outlet, theinlet is closer to an axis of rotation than the outlet; and a hubarranged on or integral with a shaft, and a shroud with blades arrangedoutside the hub around the periphery thereof, and a gap is providedbetween the hub and the blades of the shroud.
 13. The impeller accordingto claim 12, wherein the gap is formed between the inner edges of theblades of the shroud and the outer surface of the hub, from the inletside of the impeller.
 14. The impeller according to claim 10, whereinfor impellers having several blades the impeller blades are perforatedfor at least a number of blades, preferably said perforations forneighbour blades are not coaxial as seen along an axis parallel to theshaft and preferably perforations of neighbour blades are not on thesame circle of rotation around the shaft.